This HMM describes the smaller, monomeric form of phenylalanine-4-hydroxylase, as found in a small number of Gram-negative bacteria. The enzyme irreversibly converts phenylalanine to tryosine and is known to be the rate-limiting step in phenylalanine catabolism in some systems.
This family is of biopterin and metal-dependent hydroxylases is related to a family of longer, multimeric aromatic amino acid hydroxylases that have additional N-terminal regulatory sequences. These include tyrosine 3-monooxygenase, phenylalanine-4-hydroxylase, and tryptophan 5-monoxygenase.